1. Field of the Invention
The present invention relates to an apparatus for manufacturing a master-disc using an electron beam irradiated to a substrate and further to an optical disc replicated from the master-disc.
2. Description of the Related Art
In recent years, there are under development of various kinds of optical discs with a large capacity such as a DVD (Digital Versatile Disc) capable of recording image/audio data and digital data thereon. Research and development are now under progress for increasing the recording capacity to, for example, 30 Gbytes for one optical disc having a diameter of 12 cm.
There is a conventional mastering or cutting process for manufacture of a master-disc which involves a laser beam of a visible or ultraviolet wavelength range. However, such a conventional method is limited in recording resolution of pits by the diameter (about 0.2 μm) of the laser beam spot illuminated on a substrate, in other words, the wavelength of used laser beam and the numerical aperture NA of used objective lens in the laser cutting machine limit the resolution.
Thus, investigations of electron beam cutting (electron beam exposure) have been made for a master-disc-manufacturing apparatus using an electron beam to produce a high density master-disc increased in the recorded data density thereon, since the diameter of the electron beam focused on the substrate can be smaller than that of the visible or ultraviolet laser beam.
The high density master-disc may having an extremely minute track pitch of 1 μm or less. In order to cutting a master-disc for an optical disc of ROM type, the spot dimensions of the electron beam to be used are decided on the basis of the dimensions of the necessary prepits.
In the master-disc-manufacturing apparatus using the electron beam, only one electron beam can be used. Therefore, there is a drawback that the mastering of minute prepits and the cutting of a wide groove for guide are incompatible with each other in the same apparatus.